The present invention relates to the field of storage and retrieval of information on magnetic media.
Presently, information is written to and read from magnetic media using thin film structures having write and read heads. The read head is typically formed of magneto-resistive material. With this type read head, it is very important to control the shape of the features of the head. In particular, the sensing surface of a magneto-resistive read head, which senses the magnetic moment of the magnetic media across an air bearing, must be flat. If there is a curvature of the surface of the read head with respect to the magnetic media, the edges of the read head or sensor will not be able to sense the information on the magnetic media.
To provide a flat or straight edge with respect the magnetic media, the air bearing surface of the thin film head is typically formed by grinding or lapping. There are several problems with this technique. The height of the head is defined by mechanical means, so there may be a problem with accurately controlling the height of the head. The other problem is that lapping into the stripe may degrade device performance by smearing the different layers together. There is also a potential for corrosion of the stripe because of the various slurries used in the lapping process.
Another approach to control head height and to avoid corrosion problems is to define a magneto-resistive strip through lithographic means and then lap up to the strip, but stop short of strip itself, leaving a very thin layer, such as 1.0 microinch or 250 Angstroms of alumina or Al.sub.2 O.sub.3, ahead of the strip. Such a recessed head structure is disclosed in U.S. patent application Ser. No. 08/541,441, filed on Oct. 10, 1995, entitled HIGH DENSITY GIANT MAGNETORESISTIVE TRANSDUCER WITH RECESSED SENSOR.
This approach has several advantages. A significant advantage is that it decreases the sensitivity of the device to environmental and process induced corrosion and allow the use of less corrosion resistant magnetic materials thereby increasing the range of materials available for use. Also, the dimensions of the read element would no longer be controlled by lapping or grinding. Furthermore, smearing of the read element layers during lapping or grinding would no longer be a problem.
There is, however, a significant process limitation associated with producing a mask defined stripe. Typically some form of conventional photolithography is used to define the structure of the stripe. For very small structures, such as 0.25 microns even advanced step and repeat cameras are near the limit of resolution. Furthermore, the trend to reduce head sizes will surely continue. Aereal density or the ability to read and write data, has been increasing 60% per year for the past 20 years. Aereal density is related to the size of the geometry of head. It is projected by this inventor, that minimum thin film head geometries will pass semiconductor geometries in year 2003 and have sub 0.1 micron structures by the year 2003.
Conventional photolithography, however, does not easily print square images well. Because of optical diffraction effects, the corners of a square shape will tend to print round. Round shapes do not form the necessary straight edge with the air bearing surface. A rounded edge will not perform well because the space between the sensing surface as it arcs away from the air bearing surface diminishes the sensing capability of the head. Extremely sharp corners and straight edges are required for small geometries.
There are several optical techniques designed to square the image, such as optical proximity correction, phase shifting, and off axis illumination. These techniques, however, are not likely to print sharp, straight edges that are needed to define very small structures. Current optical lithography techniques, therefore, ultimately will fail.
There are other techniques, not dependent upon light that may work. E-beam direct write and X-ray lithography may be able to produce the required geometries. The cost of these systems, however, is extremely high, and the technical challenge behind implementing these type systems is also extremely high.